/Engine/Source/Runtime/Engine/Public/LightMap.h
Allocates virtual texture on demand and returns it, may return nullptr if not using virtual texture 'const' method setting 'mutable' member is not amazing, but this is required to work around ordering of render commands submitted from main thread, it's possible for commands that want to access AllocatedVT from here execute before this has a chance to runInitRHI()
const [IAllocatedVirtualTexture](API\Runtime\RenderCore\IAllocatedVirtualTexture) * GetAllocatedVT() const